Interleukins (also
called lymphokines) are a sub-group of small soluable proteins
called
cytokines which function as chemical
messengers between cells. The role of interleukins is to mediate and control
the immunologic and inflamatory response.
There are at least 18 known interleukins most of which have only been discovered
in the last few years. Their role within the immune system is only beginning
to be understood and they are just starting to be utilised in the treatment
of a wide variety of diseases including cancer, AIDS and autoimmune
diseases such as multiple sclerosis and rheumatoid arthritis.

Interleukins are
largely secreted by white blood cells (leukocytes)
and received by receptors in others. The stimulation of interleukin receptors
causes the recieving leukocyte to behave in a variety of ways depending
on its type and the context. These include proliferating themselves, releasing
other cytokines, inhibiting the release of other cytokines and activating
themselves.

The interleukins
are abbreviated to IL- followed by their number, eg. IL-2. Their receptors
are suffixed with an "R" eg. IL-2R. The following table briefly describes
the role of each of the known interleukins.

Causes
activated T- and B-cells to proliferate themselves.
It also induces antibody synthesis.

Interleukin-3IL-3

T-cells

Causes
other leukocytes to be proliferated - it does this by making certain types
of stem cell in the bone
marrow to differentiate and grow. These stem cells (hematopoietic
stem cells) mature into leukocytes.

Interleukin-4IL-4

Helper T-cells

Causes
T- and B-cells to grow. It's also a factor in the production of IgE antibodies.

Interleukin-5IL-5

Helper T-cells

Stimulates
B-cells, and eosinophils. It causes B-cells
that produce IgA antibodies to proliferate

Interleukin-6IL-6

T-cells, Macrophages

Works
in combination with alpha interferon
to induce B-cell differentiation. It also causes the production of acute
phase proteins in the liver and stimulates T-cells and other leukocytes.

Acts
to inhibit some aspects of the immune system while stimulating others.
It represses the production of other cytokines within the immune system,
especially gamma interferon, TNF-alpha,
IL-1 and IL-6. It inhibits antigen
presentation but activates B-cells.